Coal Tar Shampoo: Uses, Mechanism, Application, Side Effects, and Precautions

Introduction

Coal tar shampoo is a medicated topical preparation widely used for the management of various scalp conditions, including psoriasis, seborrheic dermatitis, and dandruff. It has been utilized in dermatology for more than a century and remains a mainstay in certain treatment regimens, especially for chronic or recurrent scalp disorders. While newer synthetic agents are available, coal tar continues to hold therapeutic value due to its broad mechanism of action, ability to reduce scaling and itching, and proven efficacy in controlling symptoms.

This guide will provide a detailed overview of coal tar shampoo, including its therapeutic uses, pharmacological mechanism, application methods, potential side effects, and important precautions. The goal is to equip both healthcare providers and patients with accurate, evidence-based information to ensure safe and effective use.

Uses of Coal Tar Shampoo

1. Psoriasis of the Scalp

Coal tar shampoo is indicated for the treatment of scalp psoriasis, a chronic autoimmune condition that accelerates skin cell turnover. This rapid turnover leads to thickened, scaly plaques on the scalp. Coal tar helps slow cell proliferation, reduce scaling, and relieve itching.

2. Seborrheic Dermatitis

Seborrheic dermatitis, often associated with Malassezia yeast, results in red, inflamed skin with greasy scales. Coal tar can help alleviate inflammation and normalize keratinocyte turnover, leading to reduced scaling and irritation.

3. Dandruff (Pityriasis Capitis)

Coal tar shampoos are also used to control mild to moderate dandruff, which presents as flaking and itching of the scalp. By reducing excessive shedding of skin cells, coal tar helps maintain a healthier scalp environment.

4. Chronic Scalp Itch (Pruritus)

The anti-pruritic effect of coal tar makes it beneficial for patients with persistent scalp itching, particularly when caused by inflammatory or hyperproliferative skin conditions.

5. Adjunct Therapy

Coal tar shampoo is sometimes used alongside corticosteroid lotions, vitamin D analogs, or antifungal treatments to enhance results in refractory scalp conditions.

Mechanism of Action

Coal tar is a complex mixture of thousands of polycyclic aromatic hydrocarbons (PAHs) and phenolic compounds, derived from the distillation of bituminous coal. Its pharmacological effects stem from multiple mechanisms:

1. Keratoplastic Effect

Coal tar slows the rapid growth and division of skin cells. This keratoplastic action normalizes epidermal proliferation and reduces scaling.

2. Anti-inflammatory Properties

Coal tar modulates inflammatory mediators and cytokines, helping to relieve redness, swelling, and itching associated with scalp conditions.

3. Antipruritic Action

By reducing nerve stimulation in the skin and suppressing inflammation, coal tar helps diminish the urge to scratch.

4. Antimicrobial Activity

Coal tar possesses mild antifungal and antibacterial properties, which may contribute to its effectiveness in seborrheic dermatitis where microbial overgrowth plays a role.

5. Photosensitizing Effect

Coal tar increases skin sensitivity to ultraviolet (UV) light. This property has been utilized in combination with phototherapy for psoriasis, but also means users should take care to avoid excessive sun exposure.

Application and Dosage

The application of coal tar shampoo should follow the manufacturer’s instructions and any advice from a healthcare professional.

1. General Guidelines

Frequency: Usually applied 1–3 times per week for chronic conditions.
Duration of Treatment: Coal tar shampoo can be used for several weeks to months, depending on response and tolerance.
Amount: Apply enough shampoo to create a rich lather and cover the entire scalp.

2. Step-by-Step Application

Wet hair and scalp thoroughly.
Apply a small amount of shampoo directly to the scalp.
Massage gently into the scalp for several minutes.
Leave the shampoo in place for 3–5 minutes (unless otherwise directed).
Rinse thoroughly with warm water.
Repeat if recommended.

3. Special Considerations

For severe scaling, a pre-treatment with keratolytic agents (e.g., salicylic acid) may enhance penetration.
Avoid contact with eyes, mouth, and broken skin.
Coal tar shampoo should not be used immediately before significant sun exposure due to photosensitization.

Side Effects

Common Side Effects

Scalp Irritation: Mild redness, itching, or burning sensation may occur.
Dryness or Oiliness: Changes in scalp oil balance can result in dryness or greasiness.
Odor: Coal tar has a distinctive, strong smell, which some patients find unpleasant.
Hair Discoloration: Light-colored hair may experience temporary staining or darkening.

Less Common Side Effects

Acneiform Eruptions: Small bumps may appear on the skin due to follicular irritation.
Contact Dermatitis: Some individuals may develop an allergic skin reaction.

Rare but Serious Side Effects

Photosensitivity Reactions: Increased sensitivity to sunlight may cause burning or rash.
Systemic Toxicity: Extremely rare with topical use, but possible if applied to large body areas over prolonged periods.

Precautions and Warnings

1. Skin Sensitivity

Patients with highly sensitive skin should perform a patch test before starting treatment to check for allergic reactions.

2. Sun Exposure

Due to the photosensitizing effect, avoid prolonged or intense sun exposure for 24–48 hours after use.

3. Open Wounds and Broken Skin

Coal tar shampoo should not be applied to raw, infected, or ulcerated skin as it can increase irritation.

4. Pregnancy and Breastfeeding

Pregnancy: Safety data is limited. Use should be based on a risk-benefit assessment by a healthcare provider.
Breastfeeding: Avoid applying to areas that could come into direct contact with a nursing infant.

5. Pediatric Use

Coal tar products are generally not recommended for children under 12 without medical supervision.

6. Long-Term Use

Although there is some theoretical concern regarding carcinogenicity due to PAHs, topical therapeutic concentrations in coal tar shampoos have not been conclusively linked to cancer when used as directed.

Drug Interactions

Coal tar shampoo is applied topically, and systemic absorption is minimal. Therefore, clinically significant drug interactions are rare. However:

Avoid using with other topical irritants or harsh hair treatments to reduce cumulative irritation.
When combined with phototherapy, use under medical guidance to prevent overexposure.

Patient Counseling Points

Use coal tar shampoo exactly as directed for the prescribed condition.
Expect gradual improvement—full benefits may take weeks.
Rinse thoroughly to avoid residual staining or odor.
Report persistent irritation or allergic reactions to a healthcare professional.
Store in a cool, dry place, away from direct sunlight.

Clinical Perspective

Coal tar shampoo remains an important, cost-effective treatment for certain chronic scalp conditions, especially when newer agents are ineffective or not tolerated. Its multi-target mechanism—addressing keratinocyte proliferation, inflammation, and itching—provides broad therapeutic value. However, patient adherence can be influenced by its odor, potential staining, and cosmetic acceptability.

Dermatologists often recommend alternating coal tar with other medicated shampoos (e.g., ketoconazole, zinc pyrithione, or salicylic acid) to improve outcomes and reduce side effects.

FAQs

1. How long can I use coal tar shampoo?
It can be used for several weeks to months under medical supervision, but long-term continuous use should be periodically reviewed.

2. Does coal tar shampoo cure psoriasis or dandruff?
No. It helps control symptoms but does not cure the underlying condition.

3. Can I use regular shampoo after coal tar shampoo?
Yes, a mild non-medicated shampoo can be used afterward to improve cosmetic feel and scent.

4. Is coal tar shampoo safe for color-treated hair?
It may cause discoloration in light or dyed hair, so caution is advised.

Conclusion

Coal tar shampoo is a time-tested treatment with proven benefits for psoriasis, seborrheic dermatitis, and dandruff. When used correctly, it offers symptom relief and improved scalp health. Awareness of proper application, possible side effects, and precautions ensures safe and effective use for most patients.

References

https://www.mayoclinic.org/drugs-supplements/coal-tar-topical-route/description/drg-20067572
https://www.dermatologytimes.com/view/coal-tar-old-treatment-new-respect
https://www.uptodate.com/contents/treatment-of-psoriasis-in-adults